Because the LED (Light Emitting Diode) offers advantages of power savings, high emission efficiency and long life, it is widely used in various applications, such as traffic control devices, electronic billboards, light of transportation, flashlights, and illumination devices.
One problem posed by use of an LED in an illumination device is that the characteristics of an LED are different from a conventional bulb. That is, a conventional bulb is a surface light source, while an LED is a point light source. Therefore, a conventional bulb can provide a 360 degree is viewing angle, but an LED can only provide a 120 to 140 degree viewing angle. Conventional techniques for overcoming this limitation include utilizing secondary optics, arranging the LEDs or polishing the lamp cover for covering the LEDs. However, even when utilizing secondary optics or providing a polished lamp cover, a conventional LED illumination device is still limited to providing a 160 degree viewing angle. People skilled in the art often arrange or assemble the LEDs to extend the viewing angle.
FIG. 1 and FIG. 2 show a conventional LED illumination device 1 as disclosed in Taiwan Patent Publication No. TW200708684. The conventional LED illumination device 1 includes a lamp cover 11, a lamp holder 12, a heat dissipating pillar 13 and three emitting units 14. The lamp cover 11 has an opening portion 111. The lamp holder 12 connects to the opening portion 111. The heat dissipating pillar 13 is mounted on the lamp holder 12, and is disposed in the lamp cover 11. Three emitting units 14 are mounted on the heat dissipating pillar 13. The heat dissipating pillar 13 is formed as a triangular body and has three slots 131 disposed apart and facing different directions. Each emitting unit 14 has a circuit board 141 and a plurality of LEDs 142. The circuit board 141 is mounted in the slot 131 of the heat dissipating pillar 13. The LEDs 142 are arranged and mounted on the circuit board 141. Consequently, the LEDs 142 emit light toward different directions.
The three emitting units 14 are arranged 120 degrees apart and each emits light in a different direction. The circuit board 141, however, is conventionally a printed circuit board, metal core printed circuit board (MCPCB), ceramic substrate (Al2O3, LTCC or AlN) or metal complex material which cannot be bent. Therefore, the LEDs 142 on each circuit board 141 are arranged on a single plate and emit light toward a single direction. The viewing angle of the conventional LED illumination device is still limited, and unable to provide a 360 degree viewing angle.
Therefore, it is necessary to provide an LED illumination device capable of overcoming the above limitations.